A motorized tower crane, powered by a single M-motor, with a 3 way gearbox that actuates the boom turntable, trolley, and hoist separately.
This was a good exercise in developing compact geartrains... hope you like it!

I managed to fit most of the gears within the 5X5 structure, so even in this tower structure there is no wastage of internal space. This is the kind of compact design that I'm very fond of... (:

Another photo to emphasize the compactness of the geartrain within the tower. I must say that I used a very large variety of LEGO Technic gears for this MOC.

Shift the lever to this position to adjust position of trolley

Shift the lever to this position to adjust height of hook

Shift the lever to this position to adjust orientation of boom

This is the drivetrain that controls the trolley movement and hook position.

The trolley is driven by: 32L axle driving a worm gear (which can slide freely along the axle, allowing the trolley to move). The worm gear drives a spur gear which is connected to the rack, propelling the entire trolley as the spur gear rotates.

The boom and the tower can be quickly disassembled. The 2 stud long worm gear has 1 stud axle engagement connecting it to the boom, and 1 stud axle engagement from the shaft coming out of the turntable. This way, the worm gear will stay in place even when disassembled.

Same backdrop, but taken without flash this time.

The crane was placed right next to the parapet on the 11th floor of a flat for this shoot.

The wind was blowing quite strongly! Luckily it was blowing inwards and not outwards... but still the crane was shaking alarmingly at times :O

Mr Koala is petrified of heights!

Overall I am pretty happy with this MOC and won't be dismantling it any time soon... (:

Nice job! I like how you used a gearbox to select the functions, rather than simply using multiple motors -- similar to how LEGO would implement it in an official set. This is at least the second impressive Technic crane we have seen here on MOCpages in just few days -- there must be something in the air ;-).